The present invention relates to a process for preparing 3-pyrrolidinol or a salt thereof, and more particularly relates to a process for preparing 3-pyrrolidinol or a salt thereof efficiently and economically. 3-Pyrrolidinol is important as an intermediate for preparing calcium blockers, .beta.-lactam antibiotics, and the like.
Hitherto, as processes for preparing 3-pyrrolidinol derivatives, there have been known the following processes:
(1) a process in which an N-substituted 3-pyrroline having the formula (III) is hydroxylated according to hydroboration to produce a compound having the formula (IV) [Journal of Organic Chemistry, 51, 4296(1986) or Synthetic Communications, 13, 1117(1983)], ##STR3## wherein R is a substituent
(2) a process in which 1-benzyl malic acid imide having the formula (VI) is prepared from malic acid having the formula (V) as a starting material, and the obtained 1-benzyl malic acid imide (VI) is reduced to give 1-benzyl-3-pyrrolidinol having the formula (VII) [Japanese Unexamined Patent Publication No. 63652/1986 or Synthetic Communications, 15, 587(1985)], ##STR4##
(3) a process in which hydroxyproline having the formula (VIII) is decarboxylated to produce 3-pyrrolidinol (II) [Chemistry Letters, 893(1986)], ##STR5## and the like.
However, in the process (1) wherein hydroboration is conducted, and in the process (2) wherein malic acid is used as the starting material, it is necessary to use relatively expensive reagents such as diborane and lithum aluminum hydride. In addition, the process (2) has a disadvantage such that even if optically active malic acid is used as a starting material, racemization occurs partly in a stage of cyclization, consequently, optical resolution must be conducted lastly in order to obtain optically pure 3-pyrrolidinol. Also, the process (3) wherein decarboxylation of hydroxyprolin is conducted has a defect such that hydroxyprolin itself is expensive. Accordingly, all of the processes (1) to (3) are unsatisfactory as the process for practically preparing racemic 3-pyrrolidinol as well as optically active 3-pyrrolidinol.
An object of the present invention is to provide an industrial preparation process of 3-pyrrolidinol, particularly optically active 3-pyrrolidinol, which is economical, simple, easy and efficient.
This and other objects of the present invention will become apparent from the description hereinafter.